1. Field of the Invention
This invention is drawn to the process for making oilfield drill pipe. In the process of making oilfield drill pipe one end of a cylindrical pipe is ‘upset’, that is made to a larger diameter and greater thickness than the original pipe. This allows for the pipe to be welded directly to an oilfield tool joint, as is well known and is shown, for example, in FIG. 1 of U.S. Pat. No. 6,244,631, incorporated by reference herein. During the upsetting process, one end of the pipe is preheated and then run through a forging process which increases both the outside diameter and the wall thickness of its end, while typically (but not always) reducing its inside diameter. This allows the upsetted end of the drill pipe to later be welded directly to the end of a tool joint which is then typically threaded in a later machining process. Most often, the upsetting process involves two or sometimes three stages of upsetting, and is typically performed at temperatures in the 2000 to 2350 degrees F. range. The process is then repeated to upset the other end of the drill pipe in a similar manner.
Pipe to be upset is staged upon one or more pipe racks on one side of the forging building and is run width-wise in a continuous process through the pre-heating and upsetting operations. The pipes are then delivered to the far side of the building for further processing. As stated earlier, the upsetting may be a two stage or a three stage process depending upon the type of pipe. Many of the sizes and types of pipes that require a three stage upsetting process cool rapidly during the upsetting process, making them too cool to be properly upset through the third phase of the upsetting without re-heating. In the past, for these types of pipe, the entire manufacturing process for upsetting the pipe would have to be re-tooled and/or reconfigured for the third upsetting, a re-tooling operation which could take 4-8 hours. Once the re-tooling was complete, the entire lot of partially upset pipes is transported around the building and run through the forging process (as described above) for a second time to perform only the third upsetting stage needed to complete the upsetting process. As a result of this present process, pipes requiring a third upsetting stage were generally required to make two full trips through the entire pipe upsetting process to upset just one end, and four full trips through to upset both ends.
2. Description of the Related Art
The present process in the manufacture of oilfield drill pipe is to produce a cylindrical thick-wall pipe of thirty feet or so in length which has tool joints welded on each end. Typically the metallurgy and chemistry of the pipe and tool joints are different, as the tool joint must be able to tolerate the repeated make up and break out of its threaded ends as the drill pipe is raised and/or lowered into a well bore. Since the diameter and thickness of the end of the tool joint are generally greater than that of the drill pipe, the end of the drill pipe are ‘upset’ in an upsetting process to make the inside and outside diameters of the ends of the drill pipe match those of the tool joint.
When upsetting the pipe ends, the preferred temperature range for forging is usually between about 2000 and 2350 degrees F. After the pipe end is heated to the correct temperature it is delivered to the upsetter where the pipe end is moved into a series of progressive die pockets in the upsetter and progressively shaped in a forging process designed to achieve the final inside and outside diameters of its end. Because time is elapsing after the pipe leaves its heat source, the temperature is decreasing. Also, the dies themselves tend to cool the pipe end. Due to mass, most sizes and type of pipe products are able to maintain enough heat to complete the forging process on the first run through. However, depending upon the initial and final dimensions of the pipes and other factors, the ends of some types of pipes will fall below acceptable forging temperature before the final forging dimensions are achieved. In these cases each pipe must again be transported though the entire process, re-heated and forged to final dimensions. It should be noted that not all types of pipe need to be re-heated and re-forged during the upsetting process. However, for those pipes that do need re-heating for the final forging operation, the entire lot of pipe is generally run through the heat and forge cycle twice for each end—or four times all together—disrupting the existing process flow and greatly reducing the efficiency.
Re-heating the end of the pipe inline would eliminate the necessity of transporting the pipe through the entire process a second time.